Cut the sirloin steak into strips about 1" x 1/4" (2.5 cm x 0.5 cm) and coat with the 1 1/2 tsp. (7 mL) flour.
Melt the butter in a heavy skillet and saute the floured meat strips on all sides.
Add the sliced onion and continue sauteing until onion is soft.
Remove both meat and onion and keep warm.
Blend the rest of the flour into pan drippings: stir until smooth.
Gradually stir in the next 5 ingredients.
Cook over medium heat, stirring constantly, until sauce is smooth and thickened.
Reduce the heat and blend in the sour cream, mushrooms and sherry.
Heat thoroughly, stirring.
Add the meat and onions and mix.
Do not allow to boil.
Serve on hot rice.